Electric lamp manufacture



Sept. 20, 1949.

J. A. M. VAN LIEMPT ETAL ELECTRIC LAMP MANUFACTURE Filed A ril 27, 1946 llllllllllilfllltillilllllllllllillla w BERGMANS MMMV THEIR ATTORNEY Patented Sept- 20, 1949 ELECTRIC LAMP Johannes Antonius Maria van Liempt and Jan Bergmans, Eindhoven, Netherlands, assignors to Generalv Electric Company, Schenectady,

Application April 27, 1946, Serial No. 665,396

In the Netherlands February 3, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires February 3, 1962 2 Claims.

In electric incandescent lamps filled with one or more rare gases there sometimes occurs the phenomenon that in them a premature arc is produced, due to which the lamp becomes unsuitable for further use. One expedient utilized in the incandescent lamp industry in order to remove this drawback consists in adding to. the gas filling whichcontains one or more rare gases, such-as argon, krypton and the like and whose breakdown voltage is comparatively low, another gas having a higher breakdown voltage. As such is frequently taken nitrogen which is present in the gas filling of ordinary incandescent lamps to a percentage of less than 25%, according to circumstances. In order to increase the breakdown voltage in such lamps still further, it would be possible to increase this percentage of nitrogen but this would have an excessively harmful effect on the favourable economy of the lamp in question, which is due inter alia to the use of these rare gases. The addition of nitrogen in the ordinary percentages is, however, not always eflicacious; in spite of the presence thereof breakdown notwithstanding still occurs sometimes in such incandescent lamps. y

We have arrived at the recognition that this breakdown phenomenon may also be due to the presence of harmful 'dust particles within the lamp. The invention is based on this recognition and it consists of an incandescent lamp wherein the gas filling contains at the most 20% of nitrogen and which is characterized by the fact that it does not contain such harmful dust particles.

These harmful dust particles, which may be constituted, for example, by glass splinters which originally adhered to the glass tubing utilized in the lamp and were dislodged therefrom during some heating or other'of the lamp, may reach the filament of the lamp and, when the lamp is or is being switched into circuit, they give of! by decomposition some metal vapour, due to which the possibility of the production. of an are considerably increases. This phenomenon is not limited to the presence of glass dust within the lamp; it may be caused by dust particles of the most diflerent nature, even organic particles are capable thereto. In the latter case there apparently occurs decomposition of the organic substance as soon as the latter enters into con- 2 tact with the filament switched into circuit. In this case there may be produced determined gases by which the breakdown is facilitated.

The said dust particles are generally at rest on any of the internal parts of the lamp oron the inside of the bulb. When, however, the lamp is given a push or is exposed to vibration, there exists the possibility that the dust particles are dislodged and float about in the interior space of the lamp. When they come in the neighbourhood of the filament and settle thereon and-when the latter is or is being switched into circuit, they may give rise to the above-mentioned harmful phenomenon.

During the manufacture of the lamp the risk of the dust particles being dislodged from the parts of the lamp which originally carried them exists when the lamp is being exhausted, for in this case the extremelythih film of moisture which initially retained the particles evaporates owing to the heat to which the lamp is exposed during 'exhaustion and these particles get a greater chance of being dislodged and of floating about in the interior space of the lamp. According to the invention,v by ensuring that the lamp is free from these harmful dust particles, breakdown due to the presence of these particles can no longer occur, owing to which, in comparison with the usual gas filled incandescent lamps, the quality of the lamp is considerably improved.

- The presence of harmful dust particles within the lamp may be ascertained by causing these particles to float within the lamp, which may be achieved, for example, by tap-ping the lamp a 4 few times against the palm of the hand. If immediately thereupon a narrow concentrated beam of'light (the so-callcd Tyndall-cone) is caused to pass through the lamp in a completely dark space whilst, for example by the use of screens of :proper shape, it is ensured that the observer cannot see the parts of the beam which are located outside the lamp, white particles are seen floating in the interior of the lamp if the latter contains harmful dust particles. If on the contrary, according to the view on which the present invention is based, the lamp is free from harmful dust particles, no white particles are visible in the said beam of light in the lamp vessel.

If in the lamp according to the invention red phosphorus is utilized as a getter, there are visihis in the Tyndall-cone red particles (the phosphorus) which do not constitute, however, harmful dust particles according to the invention; if, on the contrary, red phosphorus is not utilized in the lamp, the said beam of light in the interior of the lamp vessel is, according to the invention, optically empty.

The invention isparticularly important for lamps comprising a doubly or multiply coiled filament since in such type lamps the possibility of a premature breakdown is greater than in lamps comprising a singly coiled filament.

According to one favourable form of construction of the lamp according to the invention the percentage of nitrogen present in the gas filling is less than which is naturally greatly beneficial to the economy (efliciency) of the lamp since owing to the absence of harmful dust particles the percentage of nitrogen, which always has a harmful effect on the economy of the lamp, may be taken very low. For the sake of illustration it may be observed that it has been found even possible to construct lamps having a filling of rare gas consisting of argon and designed for an operating voltage of 220 volts, with a content of nitrogen of less than 1%.

Another form of construction of the lamp according to the present invention is characterized in that the bulb of the lamp has an internal volume in cc. of the order of magnitude of W+25 or less, where W is the wattage of the burning lamp. It may be observed in this connection that the internal volume in cc. of the bulb of an ordinary incandescent lamp filled with argon amounts to about 2W+50. With the means usually cmployed it has proved to be impossible to reduce this volume to a high extent for lamps provided with the ordinary gas fillings such as argon since it has been found that the risk of breakdown is increased to an inadmissible extent. By proceeding in accordance with the invention it is also possible to construct lamps containing a filling of argon with a very small bulb, which involves, with the same gas pressure. a considerable economy in filling gas.

Besides, the invention is particularly important for lamps filled with krypton and/or xenon since the temperature of the filament is higher than in argon lamps and since krypton has a lower breakdown voltage than argon. For these reasons the usual krypton lamps always contain a higher content of nitrogen than incandescent lamps. By proceeding in accordance with the invention and by adding to the krypton, for example, only 5% of nitrogen, which is possible owing to the absence of harmful dust particles, it is possible to obtain the full benefit of the advantageous properties of krypton.

In order to free the lamps according to the invention from dust, various methods may be ap plied. According to the invention, all the components of the lamp may be manufactured in surrounding atmospheres which are completely free from dust whilst the lamps may also be constructed from these components in such a surrounding atmosphere. According to a different method according to the invention of manufacturing such lamps a current of gas free from dust is caused, prior to the filling of the lamp, to pass through the latter while the lamp is being heated and submitted to a vibratory or jerky motion. All the dust particles are thus dislodged from the wall and the internal parts of the lamp and carried along with the washing gas. Then the lamp is filled with the filling gas in'question and sealed off. In this case it is desirable either to utilize no phosphorus at all on the coil but to have recourse to other getters or to provide the phosphorus in a particular manner in the lamp so that it cannot be dislodged. In the first case the coil may be heated during the washing operation without any objection.

According to the invention, it is also possible that when the lamp is being alternately exhausted and filled, the so-called "washing operation," a vibratory or jerky motion is imparted to the lamp in heated condition, owing to which the dust is dislodged and carried along in the same manner. This method is particularly important 7 possible, prior to the sealing-in operation, to blow the components of the lamp such as the bulb and the stem in heated condition with air free from dust, for example by means of a blower by which dust-free air is blown into the annular slit between the stem and the bulb which have already been centered relatively to one another, whereupon these parts are sealed to one another at once and the lamp is further completed.

Such an arrangement is shown in the accompanying drawing wherein i and 2 are the bulb and the stem respectively of the lamp to be manufactured. The means of support for the bulb I are not shown; the stem bears upon the table. The blower 5 is arranged in the annular slit 4 between the bulb and the stem so as to be slidable in the vertical direction. It consists of two coaxial cylinders which are connected to one another at the top by means of a perforated wall 6.

While the lamp parts i and 2 which are to be connected to one another, are being heated to a temperature of about 400 C. and submitted to a vibratory motion, the blower 5 blows a dustfree gas, for example dust-free air, into the space between the bulb i and the stem 2. This gascurrent carries along with it dust particles adhering to these parts and escapes from this space, according to the arrows shown, between the outside of the blower 5 and the inside of the bulb I while carrying the harmful dust particles along with it. By moving the blower 5 up and down during this treatment all the parts of the lamp are washed by the dust-free gas. After this treatment the blower is lowered and the bulb l and the stem are sealed together whereupon the lamp is filled with the desired filling-gas through aifir exhaust tube 1 which is subsequently sealed 0 By utilizing this device and by mounting it on an existing incandescent lamp machine, it is possible to manufacture the lamps according to the invention in a simple manner.

What we claim is:

1. The method of manufacturing an electric incandescent lamp which comprises positioning the lamp mount in sealing-in relation within the lamp envelope, washing the mount and the interior of the envelope with a current of dustfree gas and simultaneously heating and vibrating the mount and envelope during the said washing operation to dislodge and remove dust particles lodged thereon, and then immediately sealing the mount into the envelope.

2. In the manufacture of an electric incandescent lamp, the step of washing the interior of the lamp envelope, prior to the final gas fillmg thereof, with a current of dust-free gas and simultaneously heating the lamp and vibrating it during the said washing operation to dislodge dust particles lodged within the said lamp envelope.

JOHANNES ANTONIUS REFERENCES CITED UNITED STATES PATENTS Number Lockwood Jan. 31. 1933 

